The invention relates to a spring system especially for use with the front wheel fork of a two-wheel vehicle.
The spring elements, which are known in the two-wheel industry for suspending a wheel, are usually built up in accordance with the principle of the telescope spring strut (telescope fork). In this connection, reference can be made to German patent publications 1,680,564 and 2,648,221.
The invention proceeds from air springs which are known for wheel suspensions in two-track vehicles.
An air spring essentially comprises a resilient member which is delimited by a cover plate at its upper end at the chassis and, at its lower end, a roll-off piston is attached which is fixed at the wheel. As a rule, the resilient member is provided with a support unit (support bell) attached to the cover plate in order to prevent lateral offset during spring deflection. Notwithstanding the support unit, conventional air springs cannot ensure an axial guidance of the wheel (which is to be suspended) along the spring deflection path. For this reason, the wheels or the wheel axles must be guided by guide linkages. The wheels or axles, which are suspended on the guide linkages, define an arcuately-shaped spring path. For this reason, the support unit must be elastically attached to the cover plate as shown, for example, in German patent publication 1,909,373.
It is an object of the invention to provide a shock-absorbing strut especially for a two-wheel vehicle. It is a further object of the invention to provide such a shock-absorbing strut wherein the use of guide linkages or other external guide elements is not needed.
The spring system of the invention is for a vehicle including a two-wheel vehicle. The spring system includes: first and second spring units mounted coaxially to each other; the first spring unit including a first roll-off piston and a first rolling-lobe resilient member coacting with the first roll-off piston during operation of the spring system; and, the second spring unit including a second roll-off piston and a second rolling-lobe resilient member coacting with the second roll-off piston during operation of the spring system.
The invention is based on the fact that the roll-off piston of a conventional air spring would tilt away if one would not prevent a swinging away with the aid of externally mounted guide members. An unwanted swinging away of the pistons is no longer possible even without externally mounted guide linkages because of a rigid connection of the two roll-off pistons of the two air spring elements mounted axially facing each other.
In such an arrangement, the two roll-off pistons take over the mutual guidance of the movable parts. A reliable guidance is ensured already without the use of an outer jacket.
According to the invention, both spring elements are not mounted in series one behind the other in the same direction (which would result in increased spring strength); instead, the two spring elements are configured so as to be mirror images of each other whereby an especially soft spring action results which is especially of advantage in the forward wheel fork of bicycles.
An essential effective element for configuring the differential air spring according to the invention is realized in the conicality of double roll-off pistons and/or a common outer jacket. The angle of inclination relative to the longitudinal axis of the spring is preferably 5 to 45xc2x0. Special spring characteristic lines can be realized by adapting the roll-off contour.
According to an embodiment of the invention, the air spring element operates in accordance with the push-pull principle and can be damped in that the spring element defines two separate air chambers which are connected to each other by suitable throttle elements.
The double rolling-lobe resilient member according to the invention can also be filled with a hydraulic liquid in lieu of a gas which is especially air. The hydraulic liquid is an incompressible medium. Preferably a pressure store is used in order to achieve the volume exchange, which is required when using an incompressible hydraulic medium, for the compression and expansion operation of the spring. The pressure store has a feed line into which damping elements can be connected.